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is the altimeter on the cateye AT-100 reliable ?(4 posts)

is the altimeter on the cateye AT-100 reliable ?PeterRider
Sep 29, 2002 8:57 AM
Just bought this computer, and was wondering if the altimeter is reliable.

This is why: yesterday I was on the Heartbreak Hundred century, and the website advertised for about 8000ft elevation gain. My computer calculated a bit more than 9000ft. One thing: I didn't check how to set the altitude yet, and it was wrong by about 1500ft (it said 500ft when the real altitude was about 2000ft). Does this explain the difference ? My knowledge of atmospheric statics does not go as far as altimetry measurements, so any information would be welcome !

Thanks,

Pierre
re: is the altimeter on the cateye AT-100 reliable ?B2
Sep 29, 2002 9:23 AM
Almost all of them are subject to a fair amount of error. I don't believe the relative altitude difference you describe should have any bearing on the cummulative gain claculation since the unit is only calculating differences in altitudes.

The 1,000' difference in cummulative gain could be due to a number of things. #1 is who is to say the organizers estimate is correct. Another thing that effects the cummulative total is the frequency which the unit samples. If one unit takes a sample every 20 seconds and another takes a sample every minute there can be a significant difference. I can't remember if the AT-100 lets you set the sampling interval - a lot of units do.

As a general rule of thumb, I would assume that most of the altimeter units out there will only be accurate to within 5-10%. I.e. - expect a 250' - 500' variance with 5,000' of climbing.

Good Luck,
Bryan
re: is the altimeter on the cateye AT-100 reliable ?PdxMark
Sep 29, 2002 10:11 AM
I have the same computer and mine seems to be pretty consistently within 5%, and often closer than that, based on comparisons with other altimeters and organized ride elevation postings. I bet your computer is more accurate than it appears, but there are settings that could mess things up.

I almost never set the correct starting elevation. I figure that pressure varies linearly with elevation so it doesn't matter what the starting elevation is.

The difference might have come about in 2 ways. First, you need to reset the elevation gained mesurement separately from resetting ride distance/time. If you just reset ride distance/time, you'll just keep adding onto your elevation gain. Second, there is a mode in which the elevation gain counts even when you're not riding.. (it let's you use the computer when hiking). In that mode, you could reset your elevation gain at home, load the bike on the car and drive to the ride and have 1000 feet of gain before your first pedal stroke.

Good luck.
re: is the altimeter on the cateye AT-100 reliable ?berni
Sep 29, 2002 11:36 AM
I have had a Specialised Elite wireless computer for 2 years now, and it's altitude readings are very accurate, amazingly so for such a small unit.

I ride mostly around the Alps, where altitudes are posted all over the place on little signposts.

So for example, I start the Col de La Joux Plane from the town of Samoens at 800m, and arrive at the top at 1700m, 10km later. And what is the computer cumulative altitude gain reading? Near as dammit, 900m, every time. Not bad.

Even little 'humps' as small as 5m up, are registered correctly. Pretty impressive for 50 quid.